He tried to sue the hospital for malpractice, and lost. Medical authorities in southern Guangdong province said there was no link between the vaccination and his child's condition. So he took his campaign to the media and traveled thousands of miles to Beijing by bicycle to petition the central government, without success.

Then in April, a court accepted a lawsuit filed by Mr. Liang together with the parents of two other children who had also fallen ill. The suit alleges that vaccines were to blame in all of the cases. Last week, the court began hearing the case against provincial and city health agencies and a state-owned drug company, based on laws concerning product safety and inspection.

In recent months, a series of product recalls, from pet food to tires, has sullied the image of Chinese exports abroad. At home, China also faces a drumbeat of complaints from consumers aghast at the harmful food and drugs approved by a graft-ridden regulatory system. Last year, the State Administration for Industry and Commerce received 4.6 million complaints over substandard products and services.

In this climate, plaintiffs like Liang may stand a chance of success, after years of trying. His case is part of a growing wave of consumer challenges to China's state bodies, says Liu Kaixiang, a law professor at Peking University.

"In recent years, people have the idea that if they encounter problems, they can sue the government ... [but] it's not easy for ordinary people to win these lawsuits," he says.

Spotlight on regulators

Liang's lawyer, Tang Jingling, who agrees that it's an uphill battle, says he wants to shine a spotlight on China's regulators as well as provide answers to the anguished families.

"With the efforts of these families, the case should help improve food and medicine quality," he says.

While consumer activism is on the increase in China, the legal system isn't bound by precedent and is squarely under the control of the Communist Party. That makes it hard to force change from the bottom up, though not impossible.

Vaccination programs in China have been dogged for years by fake or contaminated vaccines.

Over 300 children were hospitalized last year in Anhui province after a receiving hepatitis A shots of dubious origins. One of the children later died. Last week, police arrested a gang in northeastern China that was selling counterfeit rabies vaccines and blood proteins, according to the official Xinhua News Agency.

'Systematic' corruption

The arrests came just two weeks after the execution of Zheng Xiaoyu, China's former Food and Drug Administration chief, who was convicted of taking bribes to approve substandard medicines. Experts say this high-profile punishment may send a tough signal, but won't stamp out the practice.

"This is a systematic problem. Executing a few corrupt officials will not change the system dramatically. We need to take away the incentives for corruption," says Dr. Lo Wing-lok, former president of the Hong Kong Medical Association and an infectious-diseases specialist.

Guangdong province, where the lawsuit is underway, has suffered its own regulatory scandals.

Last year, Luo Yaoxing, the former director of the provincial health ministry's immunization institute and a prominent figure in the SARS crisis in 2003, was sentenced to life imprisonment for taking bribes from vaccine producers.

In the case of Liang's daughter Jiayi, a key question is whether the live vaccine she was given in August 2003 to prevent Japanese encephalitis, a mosquito-carried disease, was contaminated. Another possibility is that she suffered a rare catastrophic reaction. Live vaccines must be kept cool and used quickly or they can become toxic, Dr. Lo said.

The other two plaintiffs received a different vaccine in 2005 under a citywide program that parents say left the children developmentally disabled and unable to attend school. All are seeking damages from city and district health departments and the vaccine manufacturer.

Authorities deny fault

In written responses to the court in Jiangmen City, health authorities denied that they administered defective drugs and said it was a coincidence that the children had fallen sick after the vaccinations. Mr. Tang, the lawyer, said the court was expected to issue a final ruling in October.

At a military hospital in Beijing, Liang's wife Xueyun cradles Jiayi in her arms, rubbing her daughter's stiffened legs. "Sometimes she responds and she recognizes us. Occasionally she even smiles," she says.

As she comforts the child, her husband keeps up a rapid-fire account of his struggle for justice. He pulls out the laminated newsprint-lined boards that he used to draw attention to his daughter's plight on vigils outside government buildings.

Though his campaign he met the other affected families with whom he filed the joint lawsuit.

After the court agreed to hear the case, one of the other fathers sent a text message to Liang's mobile phone. "I can't sleep. I thought about it all night. They are too powerful," he wrote, referring to the defendants.

Liang suspects the vaccine was faulty and wants the authorities held to account for his daughter's condition. He scoffs at Beijing's favorite buzzword for maintaining peace and stability in a country awash in fake goods.

"The government wants a 'harmonious society'. How can they abandon their children and do nothing?" he asks.